The Influence of Single and Multiple Injection Strategies on In-Cylinder Flow and Combustion within a DISI Engine 2009-01-0660

It is widely accepted that engine combustion is fundamentally affected by the in-cylinder charge motion. Flow field structures present at the time and location of spark ignition are known to have a controlling effect on early flame development. Therefore, improved understanding of the variation in flow field structures local to the spark plug at the time of ignition is required.

This study investigates the spatial and temporal development of flow field structures within the pent roof combustion chamber of a single cylinder, direct injection spark ignition (DISI) optical engine. High speed particle image velocimetry (HSPIV) has been used to quantify the flow field leading up to and following spark ignition. HSPIV data was recorded at a rate of 5 kHz, providing a temporal resolution of 1.8 crank angle degrees (CAD) between measurement fields and a spatial resolution of 512 by 512 pixels. Velocity field measurements were acquired over a 70.2° crank angle (CA) range, from 300° CA to 370.2° CA after top dead centre (ATDC), spanning spark ignition (325° CA ATDC).

Results show the spatial and temporal development of large scale bulk flow and small scale structures up to and following spark ignition. Comparison of individual cycles highlights the variation in flow field structures within the combustion chamber and the effect this has on engine performance. The levels of turbulence that exist within each cycle have been calculated as a root mean square (RMS) velocity and compared to engine performance indicated mean effective pressure (IMEP) and mass fraction burnt (MFB). In order to determine the range of spatial and temporal scales of turbulence that affect the burn rate and IMEP, frequency analysis was carried out on the HSPIV velocity field data. The results demonstrate the link between in-cylinder high frequency turbulence and engine performance, in terms of indicated mean effective pressure and burn rate.

To assess the feasibility of using multiple injection strategies to control combustion, three different injection strategies were investigated. Single, double and triple injection strategies, occurring during the intake stroke to achieve a homogenous charge, were tested. Results indicate that even with early injection a higher level of turbulence intensity is generated within the combustion chamber at the time of ignition for the multiple injection strategies.